Shielding design is an important factor in the reliable operation of PVD tools. The shielding has to contain deposited material, to avoid deposition on the chamber walls for example, retain this material for as long as possible, ideally a full target life without release of particles, be simple to replace, be low cost and have no adverse effect on the film coating on the wafer.
Typically stainless steel shielding is used in PVD systems as robust, relatively complex assemblies can be constructed which can be simple to install in the process chamber and are relatively cost effective as they can be cleaned and re-used.
When high power deposition processes are carried out, i.e. >30 kW, the heat load on the stainless steel shielding can cause distortion (due to the fact that stainless steel is a relatively poor thermal conductor) which in turn will result in particles being ejected from the shielding. This is not acceptable for standard operating conditions. While shielding could be made from a metal with better thermal properties, e.g. Aluminium this tends to be costly to fabricate and impractical to clean. Cleaning aluminium is difficult and when tight dimensional tolerance is important (to maintain film uniformity on the wafer for example) it is not practical to re-use the material.